| Summary: | 碩士 === 國立臺灣大學 === 工程科學及海洋工程學研究所 === 103 === The ocean environment around Taiwan is very complicated. It is highly limited in collecting hydrographic data with research ships. Thus ocean is always under-sampled in the study of water-column properties. Ocean circulation models are solution to this under-sample problem. We need the information of the entire water column of the area where we carry out numerical simulations of underwater acoustic propagation and sonar performance prediction. Ocean model have ability to do nowcast or forecast of hydrographic data. In this study, the goal is to establish a joint ocean and acoustic model by combining ocean model and sound propagation model to predict sonar performance in the area of interest by solving the sonar equation.
First of all, four ocean models (HYCOM/T24/T36/Q100) are established based on Taiwan Costal Ocean Nowcast/Forecast System (TCONFS) with different boundary condition. Then the root mean square error (RMSE) between historic hydrographic data of Ocean Data Bank and outputs from each ocean model are compared to estimate the accuracy each model. The results show the accuracy of T24 model is the best.
The tidal model TPXO is superposed on T24 model to better model the real ocean. The RMSE od transmission loss between the acoustic propagation experiment data and the results of sound propagation simulation using CTD data collected during the acoustic experiment, and ocean data of T24 and TCONFS model. The RMSE from these models and the acoustic data is 3.25, 3.83 and 3.28 dB respectively. In the following sonar performance calculation, the TCONFS model id used for it resembles the ocean environment most and the RMSE of the simulation data with the experimental data is compatible.
The sonar range analysis in the east-northern sea area of Taiwan is carried out with outputs of TCONFS model. Under the assumption of noise-limited condition, that predicted sonar range varies with bathymetry, and seasonal variation is clearly seen as the seasonal variation is present in the hydrographic condition.
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